Electrical discharge device



Jan. 24, 195i) w. G. MAYER 2,495,274

' ELECTRICAL DISCHARGE DEVICE Filed Dec. 19, 1944 2 Sheecs-$heet l llll :lllll PULSE GENT FIG.

INVENTOR.

WILLIAM G. MAYER ATTORNEY Jan. 24, 1950 w. G. MAYER ELECTRICAL DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed Dec. 19, 1944 HM O m M H I ////////H/////////////// H H H fl/ H //n/// /N/ W/ 0 //////H////// /H N H /0 H FIGZ.

INVENTOR. WILLIAM G. MAY ER ATTORNEY Patented Jan. 24 1950 2,495,274 ELECTRICAL DISCHARGE DEVICE William G. Mayer, Asbury Park, N. J., assignor to the United States of America as represented by the Secretary of War Application December 19, 1944, Serial No.

4 Claims. (Cl. 250-27.5)

(Granted under the act of amended April 30, 1928;

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to ine of any royalty thereon.

My invention relates to electrical discharge devices of the mercury pool type in which the discharge is initiated by an auxiliary electrode partly submerged in a pool of mercury.

Devices of this type, commonly called ignitrons, contain a control electrode, or igniter, which is partially immersed, permanently, in the pool cathode. The igniter electrode, usually a rod of high-resistance refractory material such as boron or silicon carbide, is shaped in the form of a cone-like solid of revolution. When this rod is immersed in the mercury, the surface tension of the mercury produces a very small separation between rod and mercury below the surface of the pool. Part of the voltage applied between the igniter and the mercury pool is thus caused to act across a very thin vapor-filled space, and the electric field in that space is correspondingly high. The field ionizes the vapor and the arc starts. The cathode spot, very minute at first, immediately increases in size and rises to the surface of the pool. Thereafter the anode attracts the required electron emission from the spot and the anode current flows.

The time required for the ignition of the are by the igniter electrode is very short and is usually somewhat less than 50 microseconds, although initiating pulses of the order of 0.5 to 2 microseconds are not uncommon.

The power required for the initial discharge is quite high, the starting voltage ranging approximately from 100 to 250 volts and the starting current ranging approximately from 3 to 40 amp. But since the starting power need be applied only for about 50 microseconds, the average power (in 60-cycle service) required for ignition may be only a fraction of a watt.

It is an object of this invention to reduce the power which must be supplied to the initiating electrode or igniter to start the main discharge. This is accomplished by introducing into the initiating electrode or igniter rod, a relatively small amount of a radio-active material. Polonium, one of the break-down products of radium having great activity and moderate life, may be used. The purpose of the radio-active material is to assist in the process of ionization.

The materials used in the initiating electrode, commonly called the igniter, are usually high resistance refractories such as boron carbide or silicon carbide. The introduction of radio-active March 3, 1883, as 370 0. G. 757) material into the igniter electrode may be accomplished in a number of ways.

One method is to place the boron or silicon carbide of the electrode in a solution of a salt of the radio-active substance. The solution is then evaporated by any well known method, leaving the radio-active salt in the pores of the boron or silicon carbide.

Another method is to deposit the radio-active substance in the pores of the boron or silicon carbide by electrolysis.

Still another method is to crush the carbide crystals to small particles after which they are mixed with a small amount of the radio-active substance. A binder is then added to the mixture after which it is moulded to the-required shape and baked at the carbonizing temperature of the binder.

When the igniter electrode is in its normal position, partly submerged in the mercury pool, the surface tension of the mercury prevents intimate contact with all the irregularities of the igniter. This leaves a small separation between the mercury and the electrode below the surface of the pool. The positive potential applied to the igniter electrode acts across this very thin vapor filled space and, because of the shortness of the distance, the electric field intensity is high and ionization occurs by the direct action of this high intensity field. Ionization by this direct unassisted action of the electric field is slow and inefficient.

However, when a radio-active material is added to the igniter electrode, there exists a continuous discharge of Alpha particles, Beta high speed electrons, and extremely short X-rays across the thin vapor sheath which separates the mercury from the electrode. The impact ofthese active ionizing radiations on the mercury surface and mercury vapor molecules produces ions in the vapor film and thereby reduces the field intensity required to initiate the discharge.

For a better understanding of the invention, reference is made to th following specification of a device embodying the invention, the said specification to be read in connection with the accompanying drawings, in which,

Figure 1 is a view, partly in cross section, of a device embodying the invention, external circuit elements thereto being shown schematically, and

Figure 2 is an enlarged cross-sectional view of an electrode embodying the invention.

In Figure 1 is shown a system using an ignitron device for producing power pulses of high intensity and short duration. The ignitron discharge device is shown generally by the designation I. The anode 2 is insulated from the metal body by a glass section 3. The igniter electrode 4 dips into the mercury pool 5 which forms the cathode for the main discharge. A pulse generator I, well -known-"inrthe artysupplieswpositive pulses to the igniter electrode :4. 4 Thes'energyxfor the system is supplied by a high voltage D. C'. source not shown, connected to terminals H and I2. the condensers of which pulse forming network-is-.-well.knownin the art.

Each time the pulse generator 1 supplies a positive pulse to the igniter electrode 4a main 'dis-' charge is initiated between the mercury pool 5. The energy for this discharge is supplied by the energy storing'pulse formingfnet work 8. energy is exhausted. serves to-transfe'r the pulse-energy te-a work cir cuit such as a-higl1 frequency oscillator. Thus eachtime a-pulse is applied to "theigniter electrode 6, the energy stored in the-network 8 1s discharged as a rectangular pulseinto the Work circuit.

By providing radio-active material in the igniter electrode the ionizing "process-is-'efiected with less'energy so that the'size and cost 'of the pulse generator may'be reduced.

Referring to Figure 2 the -ele'ctrode 4 consists of a baseor core I3'of high resistance refractory material, superficially interruptedby porous depressions, and a thin coating material disposed about saidrc'ore and'imb'edded in the said porous depressions. It willbe understood that the thickness of the coating Ml is exaggerated, the said coating actually-'beingextremely thin..

Although Figure 2.v shows a complete surface coating, it will be apparent that thecompleteness of the coating is dependent upon. theaamount of radio-active material that .is used.. Irumany applications it will be suificient ifv the amount used 1 is .so small that only the porous. depressions .are filled. It will be further-apparent that the radioactive material. may .be dispersed throughout the bodycof the core-rather than being-coated on the surface thereof;

.. Although-I shave shown-tbut' :one- 11885 of and but a few methods of making aradio-active electrode, it is obvious that .other-ruseslandz methods This energy is fed through choke "coil 40 to-- the pulse aforming network: 8,.

The discharge ceases "when' this "stored The pulse transformer 9 M of radio-active 4 anode :2 andthe are possible, and the invention is to be read in the spirit of the appended claims.

I claim:

1. In a gas discharge device having an anode, a mercury cathode, and a starter electrode formed of high: resistance refractory material having an irregular ..surface..characterized by azplurality of pores partly submerged in the mercury cathode, means for reducing the energy required to initiate the -discharge; said means including a deposit of radio-active-.ma.terial v on the surface and in the pores of-the refractory material of said starter electrode, said radio-active material having a radio activity at least comparable to polonium.

'ZIThe-device "as-defined in claim 1 in which theradioactive material is polonium.

3. In a gasdischarge device for producing short pulses of electrical energy including an anode, a mercury cathode, and .a starter electrode formed of high resistance refractory material havinglan irregular surface characterized by -axplurality of pores said electrode being partly subinerged'in the mercury cathode, means for reducing the energy required to initiate the discharge/said means includinga deposit ofradio-active material on'the surface and in the pores of the 're'frac tory material of-said starter electrode;said radio-'- active material having a' radioactivity of the order cf polonium.

4. The deviceas defined in claim 3'-in-which the=radio-active material is polonium.

WILLIAM (3r. MAYER.-

REFERENCES CITED- The following references are-of 'recordinthe fiienf this patent:

UN ITED STATES .PATENTS OTHER REFERENCES Development of .Electronic Tubes/'3 by"I..-E. Mouromtseff, .vol.. 33, No; 4, April: 1945,: pp; 223- 233. 

